The goal of this project is to test the efficacy a theory based, patient-centered, dynamically tailored intervention delivered via a cell phone app. The four aims of this project are to: 1) Test the efficacy of the intervention to improve long term maintenance of osteoporosis prevention health behaviors in midlife women, 2) evaluate moderators and mediators of long-term engagement in health behaviors, 3) describe processes of health behavior change and evaluate differences within and between subjects using Ecological Momentary Assessments (EMA) as a complement to traditional measures and 4) evaluate the utility of The Individual and Family Self-Management Theory to explain health behavior change. In the U.S., over 35 million women either have or are at high risk for osteoporosis at an anticipated cost of greater than $25 billion by 2025. Osteoporosis affects 1 out of 2 White women, is rapidly growing among populations of color and causes high chronic disease burden worldwide. Less than 6% of women regularly engage in the basic health promotion behaviors. The vast disparity between the high prevalence of osteoporosis and the low number of people who engage in preventative care highlights this condition as one of many striking examples of the crucial role behavior change could play in improving health and decreasing health care costs. New knowledge suggests enhancing knowledge and beliefs, self-regulation skill and abilities, and social facilitation leads to self- management and improved health outcomes. It is hypothesized that the more an intervention integrates health behavior change processes into daily activities the more likely it is to increases one's capacity to self-manage. The work proposed is significant because it focuses on the serious and prevalent condition of osteoporosis; tests the application of a theory based, patient-centered, dynamic intervention designed to improve outcomes; and, decisively bundles new knowledge about methodologies, intervention processes, and delivery media to provide a cohesive foundation for intervention development and testing. Innovative aspects include use of EMAs as a complementary approach to providing feedback and measuring behavior change processes; testing a newly identified health behavior change theory; and development and evaluation of a cell phone app, one type of m-Health. Through technological advances we now have the capacity to integrate health behavior change processes into every day activities via a cell phone app but the effectiveness of the app to change health behaviors has not been demonstrated empirically. A three-group randomized controlled longitudinal design with data collected at baseline, 3, 6, 9, and 12 months will be used. A convenience sample of 288 (96 per group) community dwelling women will be enrolled. Outcomes will be evaluated with self-report, behavioral performance, and bio-behavioral measures, including DXA and vitamin D. The expected outcomes are achievement of an increase in women's initiation and long term maintenance of osteoporosis self-management behaviors and stabilization of bone mineral density.